ABSTRACT
The starvation-stress response (SSR) of Salmonella typhimurium encompasses the physiological changes that occur upon starvation for an essential nutrient, e.g. C-source. A subset of SSR genes, known as core SSR genes, are required for the long-term starvation survival of the bacteria. Four core SSR loci have been identified in S. typhimurium: rpoS, stiA, stiB, and stiC. Here we report that in S. typhimurium C-starvation induced a greater and more sustainable cross-resistance to oxidative challenge (15 mM hydrogen peroxide (H2O2) for 40 min) than either N- or P-starvation. Of the four core SSR loci, only rpoS and stiC mutants exhibited a defective C-starvation-inducible cross-resistance to H2O2 challenge. Interestingly, (unadapted) log-phase S. typhimurium rpoS and stiA mutants were very sensitive to oxidative challenge. Based on this, we determined if these core SSR loci were important for H2O2 resistance developed during a 60 min adaptive exposure to 60 microM H2O2 (adapted cells). Both unadapted and adapted rpoS and stiA mutants were hypersensitive to a H2O2 challenge. In addition, a stiB mutant exhibited normal adaptive resistance for the first 20 mins of H2O2 challenge but then rapidly lost viability, declining to a level of about 1.5% of the wild-type strain. The results of these experiments indicate that: (i) the rpoS and stiC loci are essential for the development of C-starvation-inducible cross-resistance to oxidative challenge, and (ii) the rpoS, stiA, and, in a delayed effect, stiB loci are needed for H2O2-inducible adaptive resistance to oxidative challenge. Moreover, we found that both stiA and stiB are induced by a 60 microM H2O2 exposure, but only stiA was regulated (repressed) by (reduced form) OxyR.
Subject(s)
Carbon/metabolism , DNA-Binding Proteins , Hydrogen Peroxide/pharmacology , Oxidative Stress , Salmonella typhimurium/drug effects , Salmonella typhimurium/genetics , Adaptation, Physiological , Bacterial Proteins/genetics , Chromosome Mapping , Drug Resistance , Mutation , Repressor Proteins/metabolism , Salmonella typhimurium/metabolism , Sigma Factor/genetics , Transcription Factors/metabolismABSTRACT
The telomeres of gorilla, chimpanzee and human peripheral blood cells have been examined by hybridization to an oligonucleotide probe, (TTAGGG)4, following conventional and pulsed-field electrophoresis procedures. The MspI site present near the chromosome terminus undergoes methylation in gorilla, chimpanzee and human genome as shown by the HpaII digestion. Minor (TTAGGG)4-hybridizing sequences have been also detected in the chimpanzee HindIII and MspI digests.
